require 'soap/wsdlDriver'
wsdl = 'http://www.dotnetsite.com/MyService/Service.asmx?WSDL
driver = SOAP::WSDLDriverFactory.new(wsdl).create_rpc_driver
puts driver.GetVals(:parameter => SOAP::SOAPInt.new(136))
Where GetVals is .Net web method to call. Generating stub files with wsdl2ruby.rb against a WSDL could what arguments you should pass.
% wsdl2ruby.rb --wsdl Foo.wsdl --type client --force
I would like to thank Hiroshi NAKAMURA for this last information